The present invention relates to a system and method for actively damping low frequency noise within an enclosure and, more particularly, to such a system and method wherein an electronic feedback loop is employed to drive an acoustic damping source within an enclosure such as an automobile cabin.
The principles of active noise control are well established and basically consist of detecting, by a microphone, the noise to be controlled, and replaying the detected noise in anti-phase via a loudspeaker so that the regenerated noise destructively interferes with the source noise. The following U.S. Patents, the disclosures of which are incorporated herein by reference, teach a variety of techniques for actively controlling noise within an enclosure: U.S. Pat. No. 5,558,298, issued to Pla et al. on Sep. 24, 1996; U.S. Pat. No. 5,535,283, issued to Susumu et al. on Jul. 9, 1996; U.S. Pat. No. 5,466,849, issued to Geisenberger on Nov. 14, 1995; U.S. Pat. No. 5,394,478, issued to Hathaway et al. on Feb. 28, 1995; U.S. Pat. No. 5,390,121, issued to Wolfe on Feb. 14, 1995; U.S. Pat. No. 5,355,417, issued to Burdisso et al. on Oct. 11, 1994; U.S. Pat. No. 5,343,713, issued to Okabe et al. on Sep. 6, 1994; U.S. Pat. No. 5,515,444, issued to Burdisso et al on May 7, 1996; U.S. Pat. No. 5,373,922, issued to Marra on Dec. 20, 1994; U.S. Pat. No. 5,310,137, issued to Yoerkie, Jr. et al. on May 10, 1994; U.S. Pat. No. 5,125,241, issued to Nakanishi et al. on Jun. 30, 1992; U.S. Pat. No. 4,689,821, issued to Salikuddin et al. on Aug. 25, 1987; and U.S. Pat. No. 4,876,722, issued to Dekker et al. on Oct. 24, 1989.
Road noise generated within an automobile cabin is commonly characterized by a number of low frequency resonant modes. This low frequency road noise is a problem because it is detrimental to occupant comfort and well being and because the sound absorbing material within the cabin does not significantly attenuate the low frequency noise. Generally, the conventional techniques referenced above have been successful in certain respects. However, none of the disclosed systems have achieved universal acceptance in the area of low frequency acoustic damping within an enclosure. Further, some of the systems have significant shortcomings. For example, the active noise cancellation system taught in U.S. Pat. No. 5,394,478 occupies a significant amount of space within the automobile and the active noise control system taught in U.S. Pat. No. 5,343,713, is related to control of noise in limited local areas within a three-dimensional space.
Accordingly, there is a need for a system and method that effectively reduces the amplitude of low frequency noise within an enclosure, particularly the enclosure of an automobile where the noise generated within the cabin is characterized by a number of low frequency acoustic modes of significant magnitude.